Mother Linda's sells it by the quart. You have to email her for availability. Last time I checked, it was $15 per quart, including shipping, with a maximum of 2 quarts. She uses only good quality, pastured pork fat from farmers local to her.

You may want to check with your local WAPF chapter leader to see if they have a recommended source. I'm getting my lard for $6 to $8 per quart. Some people have had luck too asking for pork fat at the butcher stand at Whole Foods. If available, they give it away for free, and you can render your own easily in the crockpot. Their pork isn't pastured, but it's supposed to be naturally raised and you won't have any preservatives in your own rendered lard.

I'd also suggest checking with a local farmer (if you've got a good source around you) for some. It's likely much cheaper than buying it already rendered and entirely possible that you might be able to get it for free from the farmer as well (that's what happened for me). I always figure it never hurts to ask. It's actually very easy to render lard on your own.

You'll want to either look for fat back or something like leaf lard (the fat around the kidneys).